Nutrients, irradiance, and mixing as factors regulating primary production in coastal waters impacted by the Mississippi River plume

Phytoplankton carbon fixation gene (RuBisCO) transcripts and air-sea CO2 flux in the Mississippi River plume

“…This evidence thus supports our conclusion that (42 mm) eukaryotes, particularly diatoms, were responsible for the carbon fixation and CO 2 drawdown we and others (Cai, 2003;Lohrenz and Cai, 2006) have observed in the MRP, and not picoplankton such as Synechococcus or picoeukaryotes which exist in much greater numbers throughout the plume area. Our findings also support the existing paradigm of MRP phytoplankton community dynamics, which dictates that production led by diatoms is prevalent in the mid-salinity plume where river water mixes with the Gulf of Mexico (Bode and Dortch, 1996;Lohrenz et al, 1999;Liu and Dagg, 2003;Liu et al, 2004;.…”

“…Our plume stations fall in the salinity range that other MRP papers characterize as a mixing zone, containing higher salinity than the water masses with greatest productivity (Lohrenz et al, 1999). Nonetheless, data from these stations provide a good evaluation of the relative trends of RuBisCO gene transcript concentrations among the evaluated phytoplankton groups in relation to surface CO 2 partial pressures.…”

“…While Mississippi River water entering the Gulf of Mexico has very high dissolved inorganic carbon (DIC) concentrations and is believed to be a source of atmospheric CO 2 , the region of mixing with oceanic water fosters high levels of primary productivity and inorganic carbon uptake, resulting in an area of estimated CO 2 influx to the surface ocean (Cai, 2003;Green et al, 2006;Lohrenz and Cai, 2006). Evidence indicates maximum phytoplankton biomass and primary production occurs at intermediate salinities (20)(21)(22)(23)(24)(25)(26)(27)(28)(29)(30) in the Mississippi River plume (MRP), while productivity is lightlimited in very low salinity water and nutrientlimited at the edges and outside the plume, where seawater CO 2 partial pressure (pCO 2 ) increases and approaches equilibrium with the atmosphere (Lohrenz et al, 1999). Productivity rates of the MRP are among the highest of river-influenced continental shelf systems (Cai, 2003).…”

Carbon dioxide dynamics and fluxes in coastal waters influenced by river plumes

“…However, the nearly linear DIC-to-salinity relationship indicates that net biological production rate, at least in a per-volume base, is much lower in the Amazon plume than in the Mississippi and Changjiang plumes. For example, NCP rates estimated from within plume DIC removal were 0.9-1.6 gC m −2 d −1 for the Amazon (Ternon et al 2000) and 1-8 gC m −2 d −1 for the Mississippi plume (Lohrenz et al 1997;Lohrenz et al 1999;Guo et al 2012), whereas the mixed layer depth of the former is nearly 10 times that of the latter. This conclusion is consistent with a comparison of measured biological production rates (see Table 4 of Guo et al 2012).…”

Effects of biological and physical factors on seasonal oxygen dynamics in a stratified, eutrophic coastal ecosystem

“…For example, primary production (Sklar and Turner 1981;Lohrenz et al 1990Lohrenz et al , 1999) and benthic respiration rates have been measured on limited temporal and spatial scales (Dortch et al 1994;Turner et al 1998;Rowe et al 2002). More recently, combined analysis of oxygen concentrations and stable isotopes has advanced our understanding of oxygen cycling in the northern Gulf of Mexico (Quiñ ones-Rivera et Fry and Boyd in press).…”